Recently, a high-k film made of a high-k material is used for a capacitor unit in order to increase a capacity of a DRAM.
As for the high-k film, a laminated film of oxides such as HfO2 and ZrO2 or Al2O3 and ZrO2 is used. However, in the case of using such an oxide material for the semiconductor devices, an oxygen vacancy may occur in the high-k film. If the oxygen vacancy occurs in the high-k film, a dipole is generated at an interface of the electrode or the metal gate adjacent to the high-k film and a band is bent by the dipole, which leads to a low effective work function. As a result, electrons readily flow and a leakage current is increased.
As for a technique for solving the above drawback, techniques for reducing oxygen vacancy in a high-k film by adding oxygen to a TiN film used as the electrode adjacent to the high-k film are disclosed in Japanese Patent Application Publication No. 2015-506097 and E. Cartier, et al., Appl. Phys. Lett., Vol. 95, 2009, p. 042901.
As for a DRAM capacitor, there is known a structure in which a dielectric film is formed on a lower electrode made of a TiN film and an upper electrode made of a TiN film is formed on the dielectric film (see, Japanese Patent Application Publication No. 2007-201083). As for a method for manufacturing a DRAM capacitor having a large capacity, there is known a method disclosed in U.S. Pat. No. 6,911,364. In this method, first, a mold oxide film is formed on a substrate and, then, a recess is formed by etching the mold oxide film. Next, a film serving as a lower electrode is formed at an inner wall of the recess and a field portion of the film is etched back. Then, the mold oxide film is removed by dilute hydrofluoric acid, so that a cylindrical lower electrode remains. Next, a high-k film is formed on a surface of the cylindrical lower electrode and an upper electrode is formed thereon.
However, in the case of forming a capacitor of a DRAM by the method disclosed in U.S. Pat. No. 6,911,364, the lower electrode is immersed in the fluoric acid HF during the removal of the mold oxide film and is exposed to an oxygen-based gas (e.g., O2 gas or O3 gas) serving as an oxidizing agent during the formation of the high-k film.
Therefore, the lower electrode needs to have high resistance to hydrofluoric acid and less stress change caused by the oxygen-based gas.
However, in the case of using as the lower electrode a TiN film added with oxygen which is disclosed in Japanese Patent Application Publication No. 2015-506097 and E. Cartier, et al., Appl. Phys. Lett., Vol. 95, 2009, p. 042901, it is difficult to realize high resistance to hydrofluoric acid and suppression of stress change caused by the oxygen-based gas.